Optoelectronic component with current deflected to high-gain paths comprising an avalanche photodiode having an absorbing region on a p-doped lateral boundary, an n-doped lateral boundary and an amplifying region

ABSTRACT

A three-terminal avalanche photodiode provides a first controllable voltage drop across a light absorbing region and a second, independently controllable, voltage drop across a photocurrent amplifying region. The absorbing region may also have a different composition from the amplifying region, allowing further independent optimization of the two functional regions. An insulating layer blocks leakage paths, redirecting photocurrent toward the region(s) of highest avalanche gain. The resulting high-gain, low-bias avalanche photodiodes may be fabricated in integrated optical circuits using commercial CMOS processes, operated by power supplies common to mature computer architecture, and used for optical interconnects, light sensing, and other applications.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with Government support under Agreement NumberH98230-18-3-0001. The Government has certain rights in the invention.

BACKGROUND

In the field of optoelectronics, integrated optical circuits orsubassemblies may be designed to replace their conventional electroniccounterparts in computing, signal-processing, and other devices. Thecost of fabricating large-scale optical circuits, particularly siliconphotonics, has significantly decreased in recent years. Nevertheless,all-optical devices may not yet be practical for some applications. Insome devices, high-speed and/or broadband optical components may bestrategically combined with low-power or low-cost electronic components.Photodetectors, which convert optical signals to electronic signals,play a crucial role at the interface between optical and electroniccomponents.

Optical signal levels in integrated optical circuits may be very low.First, the light sources are often low-power, both to conserve energyand to avoid dissipating enough waste heat to degrade overall deviceperformance. Second, some of the source light may be lost in thewaveguides and other optics in the circuit. Therefore, photodetectors inthese integrated optical circuits preferably function well at low lightlevels.

An avalanche photodiode (APD) is a type of photodetector in which acharge carrier produced by photon absorption enters a gain region whereit frees other charge carriers by collision. These other charge carriersalso collide in the gain region, each of them freeing multipleadditional charge carriers. For each charge carrier that enters the gainregion, many more exit to be received by downstream electronics. Thus alow-light optical input produces an amplified electrical output.

The amplification mechanism of an APD may be compared or analogous tothe operation of the photomultiplier tubes commonly used for low-levellight detection in classical optics. However, unlike photomultipliertubes, APDs can be fabricated on the miniaturized scale of integratedoptical chips, using materials and processes already characterized andused in semiconductor fabrication.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure may be better understood from the followingdetailed description when read with the accompanying Figures. It isemphasized that, in accordance with standard practice in the industry,various features are not drawn to scale. In fact, the dimensions orlocations of functional attributes may be relocated or combined based ondesign, security, performance, or other factors known in the art ofcomputer systems. Further, the order of processing may be altered forsome functions, both internally and with respect to each other. That is,some functions may not require serial processing and therefore may beperformed in an order different than shown or possibly in parallel witheach other. For a detailed description of various examples, referencewill now be made to the accompanying drawings, in which:

FIG. 1A illustrates a simplified avalanche photodiode according to oneor more disclosed examples.

FIG. 1B illustrates a more complex avalanche photodiode according to oneor more disclosed examples.

FIG. 2A illustrates the process of conversion of light tophotoelectricity and the amplification of the electricity according toone or more disclosed examples.

FIG. 2B illustrates photocurrent leakage through unshielded n-dopedlateral boundaries.

FIG. 2C illustrates charge carrier redirection through amplifyingregions by shielding n-doped lateral boundaries according to one or moredisclosed examples.

FIG. 3A illustrates simulation results for a z-oriented electric fieldin an avalanche photodiode according to one or more disclosed examples.

FIG. 3B illustrates simulation results for an x-oriented electric fieldin an avalanche photodiode according to one or more disclosed examples.

FIG. 3C illustrates simulation results for vertical photocurrent densityin an avalanche photodiode according to one or more disclosed examples.

FIG. 4 illustrates a method of fabricating an avalanche photodiodeaccording to one or more disclosed examples.

FIG. 5A illustrates a generalized computing or communication device intowhich an integrated optical circuit may be embedded according to one ormore disclosed examples.

FIG. 5B illustrates an optical module interoperating with two electricalmodules in a generalized computing or communication device according toone or more disclosed examples.

DETAILED DESCRIPTION

The description of the different advantageous examples has beenpresented for purposes of illustration and is not intended to beexhaustive or limited to the examples in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art. Further, different advantageous examples may providedifferent advantages as compared to other advantageous examples. Theexample or examples selected are chosen and described in order to bestexplain the principles of the examples, the practical application, andto enable others of ordinary skill in the art to understand thedisclosure for various examples with various modifications as are suitedto the use contemplated.

Before the present disclosure is described in detail, it is to beunderstood that, unless otherwise indicated, this disclosure is notlimited to specific procedures or articles, whether described or not. Itis further to be understood that the terminology used herein is for thepurpose of describing particular examples only and is not intended tolimit the scope of the present disclosure.

Replacing conventional integrated circuits with integrated optics maydramatically improve the speed at which a device can collect anddistribute information. However, many optoelectronic components requiremore power to run than the electronics they replace. The challenge ofproviding sufficient operating power arises, for example, whenintegrating optoelectronic subsystems into existing electronic devices.A conventional avalanche photodiode (APD) may require biasing at25V—more than twice the 12V limit of typical CMOS computer architecture.Conventional APDs' power consumption is also high due to the high biasvoltage required to achieve breakdown.

For purposes of this document, a “semiconductor” is any solid substancewith conductivity higher than that of an insulator but lower than thatof most metals. The conductivity of a semiconductor increases withtemperature and may also be increased by adding impurities (“doping”). A“substrate” is a workpiece such as a wafer, chip, optical window, orother supporting structure on which components such as the disclosedAPDs are fabricated. The substrate may include previously fabricatedlayers and/or structures underneath the level of the APD. A “layer” is astratum deposited, grown, created by doping, or otherwise formed on asubstrate or over a substrate. The term “layer” may include laminatesand other stacks as well as single-material strata. An “absorber” or“absorbing material” may be any material that absorbs light and producesa photocurrent.

“Charge carriers” shall mean those attracted to negative charges; i.e.,holes in a forward-biased device and electrons in a reverse-biaseddevice. Examples of reverse-biased devices do not preclude thepossibility of forward-biased variations. “Amplifying” refers toincreasing the amplitude of a photocurrent, such as when charge carriersreleased by absorption of photons are multiplied by collision in anamplifying region. A “terminal” may refer either to an electrode or to aconductive lead connected to the electrode.

The terms “over,” “above,” “under,” “underneath,” and “below” mayinclude “in contact with” or “separated from by intervening layers.”“Lateral” shall mean “in a direction parallel to the substrate surface.”

An APD may be considered to act upon incoming light in two ways: (1)absorbing the light, causing an initial photocurrent to flow, and (2)amplifying the photocurrent to a level usable by downstream electronics,sometimes referred to as “photomultiplication.” In some simple APDs,absorption and amplification occur in a single region of semiconductormaterial such as silicon (Si) or germanium (Ge). However, at the1300-1500 nm near-infrared operating wavelengths of silicon photonics,Ge may be more effective for absorbing photons and emitting chargecarriers, and Si may be more effective for multiplying the chargecarriers. Separating the absorbing and amplifying functions intodifferent regions (optionally with different compositions) allows thefunctions to be optimized independently rather than traded off againsteach other.

Some existing APDs, such as separate absorption charge multiplication(SACM) APDs, reduce the breakdown voltage by inserting a speciallydesigned layer of charged material between the absorbing region and theamplifying region. The charged layer concentrates the electric field inthe amplifying region, causing most of the applied bias voltage to dropacross the amplifying region. However, the charged layer is opticallylossy, and its complex doping profile requires very precise control.

Another approach to reducing bias voltage in APDs has been to add athird electrical terminal. Three-terminal APDs provide a first voltagedrop between the absorbing region and the amplifying region (e.g.,across the absorbing region) and an independently controllable secondvoltage drop across the amplifying region. One of the voltage drops maybe used to control the electric field (E-field) in the absorbing regionwhile using the other to independently control the E-field in theamplifying region. This approach may result in increased photonabsorption, which in turn increases the initially generatedphotocurrent. However, a significant fraction of this photocurrent maytravel directly from the absorbing region to a collecting region of theAPD (e.g., an n-doped region under the absorbing region). Photocurrentthat bypasses the amplifying region is not multiplied, and thereforemakes only weak contributions to the output signal.

In the disclosed examples, the generation of charge carriers takes placein a first region of the APD (e.g., an absorbing region), and theirmultiplication takes place in a separate second region (e.g., anamplification region). This allows the materials in each region to beindependently optimized for their particular functions. Moreover, thedisclosed examples use three electrical terminals to provide twoindependently controllable voltage drops. One of the voltage dropsdetermines the current flow through the absorbing region while the otherdetermines the current flow through the amplifying region. In addition,an electrically insulating layer is provided between the absorbingregion and the leakage paths that circumvent the amplifying region,redirecting more photon-generated charge carriers into the amplifyingregion to be multiplied, thus increasing the gain of the APD relative toan APD without such an electrically insulating layer.

A first surface region of the amplifying material may be p-doped to forma contact for a first terminal. A second surface region of theamplifying material may be n-doped to form a contact for a secondterminal. A surface region of the absorbing material may be p-doped toform a contact for a third terminal. The p-doped and n-doped regions ofthe amplifying material may be extended underneath the absorbingmaterial to form opposing lateral boundaries of an undoped interstice ofamplifying material. The undoped interstice between the p-doped lateralboundary and the n-doped lateral boundary is the amplifying region wherethe gain is highest. An insulating layer between the absorbing regionand the n-doped lateral boundary (e.g., disposed or formed over then-doped lateral boundary) prevents charge carriers (negative chargecarriers in a reverse-biased device, positive charge carriers in aforward-biased device) from leaking through the lowest-resistance,non-amplifying n-doped lateral boundary. Charge carriers blocked by theinsulating layer are redirected through the path of next-lowestimpedance, e.g., across or through at least a portion of the nearestundoped interstice where they are multiplied.

Optionally, multiple amplifying interstices may be formed by alternatingmultiple p-doped and n-doped lateral boundaries between the firstterminal and the second terminal. The insulating layer may then beformed over all the n-doped lateral boundaries (or formed as a blanketlayer and selectively etched away from the p-doped lateral boundaries,undoped interstices, and second terminal contact area).

The resulting APDs with enhanced gain and low bias voltage may be usedin integrated optical assemblies, combined optical/electronic circuitsand optical connections between electronic modules. They conferparticular advantages in small or crowded spaces, low-light conditions,thermally sensitive environments, or where limited operating power orbias voltage is available. APDs with enhanced sensitivity, able tooperate at the standard bias voltage of existing computer architecture,may dramatically improve the performance of integrated optics incommunication (for example, in datacom and telecom applications) andinformation collection (for example, in sensors for Internet of Things,LiDAR, quantum computing, bio/medical applications, etc.).

FIG. 1A illustrates a simplified avalanche photodiode according to oneor more disclosed examples. Three electric terminals—first terminal 113,second terminal 114, and third terminal 115—control local electric fielddistribution inside the APD by providing two different voltage dropsthat can be set independently. In a reverse-biased device, firstterminal 113 has a lower voltage than second terminal 114; in aforward-biased device, the opposite would be true.

Third terminal 115 contacts a p-doped region 105 of absorbing region106. Absorbing region 106 may be any material or layer of material thatabsorbs photons at the APD's operating wavelengths and emits aphotocurrent of charge carriers as part of the absorption mechanism. Inthe near-infrared range of 1300-1550 nm, Ge is a strong absorber and awell-understood semiconductor fabrication material. Indium galliumarsenide (InGaAs) is an alternative near-infrared absorber up to 1600 nmwavelength. Si is effective at wavelengths less than 1100 nm.

To multiply the charge carriers and amplify the photocurrent, amplifyingregion 112 is formed in a layer of semiconductor 102 by the E-fieldbetween a p-doped lateral boundary 103 and an n-doped lateral boundary104. Semiconductor 102 may be any material that readily multipliesincident charge carriers in the presence of an E-field. If absorbingregion 106 is very efficient and converts virtually all of the incidentlight into photocurrent, there is no need for semiconductor 102 to alsostrongly absorb the operating wavelength. Therefore, Si, which has verylow multiplication noise and is also among the best-known andlowest-cost semiconductor fabrication materials, may be used assemiconductor 102. InGaAs may introduce more multiplication noise thanSi, and Ge may be noisier still.

P-doped and n-doped lateral boundaries 103 and 104 are formed in a layerof semiconductor 102 (e.g., by p- or n-doping respective regions orportions of the semiconductor 102). The lateral boundaries 103 and 104are three-dimensional doped structures in the silicon with an undopedinterstice between them. Each of the p-doped and n-doped lateralboundaries 103 and 104 may include opposing sidewalls extending betweenupper and lower surfaces, respectively. As illustrated, in someimplementations, the lateral boundaries 103 and 104 may include exposedportions (e.g., outward-facing ends extending past respective lateralsides of the absorber 106) and covered portions (e.g., inward-facingends extending medially under the absorbing region 106).

The outward-facing end of p-doped lateral boundary 103 contacts firstterminal 113, while the outward-facing end of n-doped lateral boundary104 contacts second terminal 114. When a voltage drop is applied betweenfirst terminal 113 and second terminal 114, the resulting voltagedifference between the right side wall of p-doped lateral boundary 103and the left side wall of n-doped lateral boundary 104 create an E-fieldin the undoped interstice between them. The E-field causes chargecarriers passing through the undoped interstice to multiply bycollision. Thus, when such a voltage is applied, the undoped intersticebecomes an amplifying region 112 (e.g., formed between inner sidewallsof the p- and n-doped lateral boundaries).

In a reverse-biased implementation, p-doped lateral boundary 103 repelsnegative charge carriers and pushes them toward amplifying region 112,while n-doped lateral boundary 104 attracts negative charge carriers andtends to pull them away from amplifying region 112. However, insulatinglayer 124 over n-doped lateral boundary 104 (e.g., over covered portionsof n-doped lateral boundary 104) blocks the leakage path from theabsorbing region 106 through the top of n-doped lateral boundary 104.With the insulator in place, the charge carriers attracted to n-dopedlateral boundary 104 may be re-directed to cross part of amplifyingregion 112 in order to reach n-doped lateral boundary 104 from the side(e.g., as described in more detail below with respect to FIG. 2B).Insulating layer 124 may include silicon oxide, other oxides, nitrides,polymers, or doped regions (e.g., hydrogen-doped or reverse-doped). Insome implementations, insulating layer 124 may be 8-12 nm thick.

In some implementations, an undoped layer 122 of semiconductor 102 mayextend beneath p-doped lateral boundary 103, n-doped lateral boundary104, and amplifying region 112. Additionally or alternatively, anundoped layer 132 of semiconductor 102 may extend above p-doped lateralboundary 103, insulating layer 124, and amplifying region 112.

The APD structure may be fabricated on substrate 101. Substrate 101 mayhave any number and type of layers and structures underneathsemiconductor 102. In some implementations, substrate 101 may be asilicon-on-insulator (SOI) substrate with a layer of native Si, and thenative Si may be used as part of semiconductor 102. Its surface may bedoped to form p-doped lateral boundary 103 and n-doped lateral boundary104. An undoped layer 122 may be preserved underneath p-doped lateralboundary 103, n-doped lateral boundary 104, and amplifying region 112.After insulating layer 124 is formed, another undoped layer 132 ofsemiconductor 102 may optionally be formed, and absorbing region 106 maybe formed over that. In some implementations, semiconductor 102,absorbing region 106, or both may be single-crystal materials. Suchlayers may be formed by epitaxy or any other suitable method.

FIG. 1B illustrates a more complex avalanche photodiode according to oneor more disclosed examples. The part of the APD shown in this figure isan interior zone analogous to the outlined area “B” on the APD of FIG.1A.

The multiplication gain of an APD depends on the E-field in theamplifying region. This E-field is controlled by the voltage drop acrosstwo of the three electric terminals. The shorter the distance betweenthe p-doped and n-doped lateral boundaries—i.e., the narrower theundoped interstice that forms the amplifying region—the lower thebreakdown voltage required to operate the APD. Low breakdown voltagereduces the power consumed by the APD and, in some implementations,allows the APD to operate at an existing standard voltage when embeddedin a legacy device, such as the 12V common to CMOS-based architecture.

A narrow (e.g., 100-500 nm) amplifying region 112 is preferable forreducing breakdown voltage, but it may be more difficult to redirectmany of the charge carriers into a region of this size because absorbingregion 106 (see FIG. 1A) is relatively wide. One solution is to havemultiple narrow amplifying regions 112 between first terminal 113 andsecond terminal 114, as in FIG. 1B. Here, five narrow amplifying regions112 are bounded by multiple discrete p-doped lateral boundaries 103 andn-doped lateral boundaries 104, with all the n-doped lateral boundaries104 covered by insulating layer 124 to prevent leakage. As illustrated,insulating layer 124 extends entirely over some of the n-doped lateralboundaries and only partially over other n-doped lateral boundaries;insulating layer 124 may, for example, be etched or otherwise removedfrom a contact area for attaching second terminal 114. Alternatively,insulating layer 124 may extend entirely over all the n-doped lateralboundaries. In such a case, a via may be formed through insulating layer124 to allow connection of second terminal 114 to n-doped lateralboundary 104.

FIG. 2A illustrates the process of conversion of light tophotoelectricity and the amplification of the electricity according toone or more disclosed examples. In operation 251, incident photons areabsorbed (e.g., in the absorbing region) by a material that releasescharge carriers in response, creating a photocurrent. In operation 252,the photocurrent flows through the APD down the lowest-impedance path(s)available. In operation 253, the photocurrent is amplified (e.g., in theamplifying region) depending on the gain of the path it takes.Photocurrent flowing through amplifying regions is amplified, butphotocurrent flowing in other paths may not be multiplied. Finally, inoperation 254 the photocurrent exits as signal being delivered by theAPD.

FIG. 2B illustrates photocurrent leakage through unshielded n-dopedlateral boundaries. For simplicity, only one amplifying region 212, onep-doped lateral boundary 203, and one n-doped lateral boundary 204 areshown.

Photocurrents 217A, 227A, and 237A originate in absorbing region 206 andtravel into semiconductor 202. Photocurrent 217A is generated overp-doped lateral boundary 203 but is repelled by the p-doped material toflow toward and into the lower-impedance amplifying region 212.Photocurrent 227A is generated over amplifying region 212, is pulledtoward the even-lower-impedance path through n-doped lateral boundary204, but still crosses part of amplifying region 212. However,photocurrent 237A is generated over n-doped lateral boundary 204.Because all the other paths are higher-impedance, photocurrent 237Aflows straight into n-doped lateral boundary 204 without traversing anyof amplifying region 212. Depending on the construction of the rest ofthe APD, while photocurrent 237A may still be collected, it is notmultiplied and will not contribute much to the output signal.

FIG. 2C illustrates charge carrier redirection through amplifyingregions by shielding n-doped lateral boundaries according to one or moredisclosed examples. With the low-impedance leakage path directly fromabsorbing region 206 to n-doped lateral boundary 204 blocked byinsulating layer 224, the lowest-impedance path for photocurrent 237B isre-directed through amplifying region 212, where it is amplified (e.g.,in contrast to photocurrent 237A which was not amplified). Photocurrent227B emerges above amplifying region 212 but is not immediately pulledtoward n-doped lateral boundary 204 because n-doped lateral boundary 204is shielded by insulating layer 224. Therefore, photocurrent 227B takesa longer path through amplifying region 212 than photocurrent 227A ofFIG. 2A. Photocurrent 217B, which emerges over p-doped lateral boundary203 relatively far from n-doped lateral boundary 204, takes essentiallythe same path as photocurrent 217A in FIG. 2B.

Therefore, insulating layer 224 blocks non-amplifying leakage paths andredirects photocurrent from the blocked paths through the amplifyingregion (e.g., photocurrent 237B), leaves existing amplifying pathsundisturbed (e.g., photocurrent 217B), and/or increases the path ofother existing amplifying paths through the amplifying region (e.g.,photocurrent 227B). This results in an increase in gain of the APDrelative to an APD without the insulating layer 224.

FIG. 3A illustrates simulation results for a z-oriented electric fieldin an avalanche photodiode according to one or more disclosed examples.Insulating layer 324 (formed by reverse doping in this simulation),n-doped lateral boundary 304, p-doped lateral boundaries 303, andamplifying regions 312 are overlaid for reference. Dark area 334Arepresents the strongest z-oriented E-field, and white halo 344represents a weaker, but still significant, z-oriented E-field.

FIG. 3B illustrates simulation results for an x-oriented electric fieldin an avalanche photodiode according to one or more disclosed examples.Insulating layer 324 (formed by reverse doping in this simulation),n-doped lateral boundary 304, p-doped lateral boundaries 303, andamplifying regions 312 are overlaid for reference. Dark area 334Brepresents the strongest x-oriented E-field, and white halo 344Brepresents a weaker, but still significant, x-oriented E-field.

FIGS. 3A and 3B show that the E-field distribution depends strongly onthe orientation of the field. The strongest z-oriented E-field 334A inFIG. 3A is mostly concentrated in n-doped lateral boundary 304 directlyunder insulating layer 324, while the strongest x-oriented E-field 334Bin FIG. 3B is mostly concentrated in amplifying regions 312 besiden-doped lateral boundary 304.

FIG. 3C illustrates simulation results for vertical photocurrent densityin an avalanche photodiode according to one or more disclosed examples.Insulating layer 324 (formed by reverse doping in this simulation),n-doped lateral boundary 304, p-doped lateral boundaries 303, andamplifying regions 312 are overlaid for reference. Dark area 364represents the strongest vertical photocurrent density, and white halo374 represents a weaker, but still significant, vertical photocurrentdensity.

FIG. 3C shows very low leakage current through the top of lateraln-doped silicon region boundary 304, with most of the photocurrentcrossing one of the amplifying regions 312 before being collected.

FIG. 4 illustrates a method of fabricating an avalanche photodiodeaccording to one or more disclosed examples. In Operation 401, asubstrate is provided. Operation 402, forming a first layer ofsemiconductor over the substrate, may be optional depending on the typeof substrate used. For example, silicon-on-insulator (SOI) chips wouldobviate Operation 402 because SOI chips come with a top layer of nativesingle-crystal silicon. The P and N contact regions could be implantedin the top silicon layer of the SOI chip.

Operation 403 involves p-doping a first terminal region and a p-dopedlateral boundary of an amplifying region. In optional Operation 413, atleast one additional p-doped lateral boundary may be formed. Operation404 involves n-doping a second terminal region and an n-doped lateralboundary of the amplifying region. In optional Operation 414, at leastone additional n-doped lateral boundary may be formed. In Operation 405,an insulating layer is formed over all n-doped lateral boundaries (and,if necessary, removed from regions that are not n-doped lateralboundaries). For example, a thin layer of silicon oxide may beselectively deposited on top of the n-doped lateral boundaries, or aninsulating layer may be blanket-deposited over the amplifying regionsand lateral boundaries, then selectively etched away from the amplifyingregions and anywhere else it may be unwanted. The insulating layer mayinclude silicon oxide, other oxides, nitrides, polymers, or dopedregions (e.g., hydrogen-doped). In some implementations, the insulatinglayer may be 8-12 nm thick.

In Operation 406, a second layer of semiconductor is formed over thep-doped lateral boundaries and n-doped lateral boundaries. In Operation407, a layer of absorbing material is formed over the top layer ofsemiconductor. In some implementations, for these two operations, alayer of epitaxial silicon and a layer of epitaxial germanium may begrown consecutively. In Operation 408, a top region of the layer ofabsorbing material is p-doped to use as a contact for the thirdterminal. Finally, in Operation 409, electrical connections are formedto the absorbing region, the p-doped lateral boundaries, and the n-dopedlateral boundaries.

FIG. 5A illustrates a generalized computing or communication device intowhich an integrated optical circuit may be embedded according to one ormore disclosed examples. An absence of any of the illustratedcomponents, however, does not remove a device from the scope of thedescription. Any or all of input/output (I/O) interface 501, processor502, data store 503, dynamic memory 504, or communications link 505 mayincorporate embedded integrated optical subsystems, connections, orsensors.

FIG. 5B illustrates an optical module interoperating with two electricalmodules in a generalized computing or communication device according toone or more disclosed examples. Optical module 511 connects electricalmodules 512 and 513. Each one of electronic modules 512, 513 controlsthe generation of light from a light source 521, such as a diode laseror light-emitting diode. For example, light source 521 could bemodulated to encode messages. Each one of electronic modules 512, 513monitors the output of a photodetector 531, such as one of the disclosedAPDs. One of the simpler examples is where electronic modules 512,513are distributed components such as memory arrays or processor cores andoptical module 511 is a fast communications link between them.

In some implementations, such as sensors, a single APD or APD array maybe packaged by itself and coupled directly to an electronics module. Forexample, the APD may sense light directly, or optionally through aprotective faceplate or filter, and the electronics analyze and outputor use the signal level. The light may be ambient light or from a sourceoutside the APD's device.

Not all features of an actual implementation are described in everyexample of this specification. It will be appreciated that in thedevelopment of any such actual example, numerous decisions may be madeto achieve the developer's specific goals for a particularimplementation, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a developmenteffort, even if complex and time-consuming, would be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

Certain terms have been used throughout the description and claim torefer to system components. As one skilled in the art will appreciate,different parties may refer to a component by different names. Thisdocument does not intend to distinguish between components that differin name but not function. In this disclosure and claims, the terms“including” and “comprising” are used in an open-ended fashion, and thusshould be interpreted to mean “including, but not limited to.” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect wired or wireless connection. Thus, if a first device couples toa second device, that connection may be through a direct connection oran indirect connection via other devices and connections. The recitation“based on” is intended to mean “based at least in part on.” Therefore,if X is based on Y, X may be a function of Y and any number of otherfactors.

The above discussion is meant to be illustrative of the principles andvarious implementations of the present disclosure. Numerous variationsand modifications will become apparent to those skilled in the art oncethe above disclosure is fully appreciated. It is intended that thefollowing claims be interpreted to embrace all such variations andmodifications.

We claim:
 1. An avalanche photodiode comprising: an amplifying region ona substrate; a p-doped lateral boundary on a first side of theamplifying region; a first terminal coupled to the p-doped lateralboundary; an n-doped lateral boundary on a second side of the amplifyingregion; a second terminal coupled to the n-doped lateral boundary; anabsorbing region on the p-doped lateral boundary, the n-doped lateralboundary, and the amplifying region; a third terminal coupled to theabsorbing region; and an insulating layer between the absorbing regionand the n-doped lateral boundary.
 2. The avalanche photodiode of claim1, further comprising a p-doped contact region between the absorbingregion and the third terminal.
 3. The avalanche photodiode of claim 1,further comprising an undoped layer between the substrate and a sharedbottom surface of the p-doped lateral boundary, the n-doped lateralboundary, and the amplifying region.
 4. The avalanche photodiode ofclaim 1, further comprising an undoped layer between the absorbingregion and a shared top surface of the p-doped lateral boundary, then-doped lateral boundary, and the amplifying region.
 5. The avalanchephotodiode of claim 1, wherein the substrate comprises asilicon-on-insulator wafer.
 6. The avalanche photodiode of claim 1,wherein the amplifying region between the p-doped lateral boundary andthe n-doped lateral boundary is 100-500 nanometers wide.
 7. Theavalanche photodiode of claim 1, wherein the amplifying region comprisessilicon, and the absorbing region comprises germanium.
 8. The avalanchephotodiode of claim 1, wherein the insulating layer comprises at leastone of an oxide, a nitride, a polymer, or a doped region.
 9. Theavalanche photodiode of claim 1, wherein the insulating layer is 8-12 nmthick.
 10. A method of fabricating an optoelectronic component, themethod comprising: p-doping a semiconductor to form a first contact anda p-doped lateral boundary for an amplifying region; n-doping thesemiconductor to form a second contact and an n-doped lateral boundaryfor an amplifying region; forming an insulating layer over the n-dopedlateral boundary; forming an absorbing region over the p-doped lateralboundary, the n-doped lateral boundary, and the amplifying region;p-doping the absorbing region to form a third contact; and formingconnections to the first contact, the second contact, and the thirdcontact.
 11. The method of claim 10, wherein the semiconductor comprisesa native silicon layer of a silicon-on-insulator substrate.
 12. Themethod of claim 10, wherein the p-doping of the semiconductor furthercomprises forming at least one additional p-doped lateral boundary, andthe n-doping of the semiconductor further comprises forming at least oneadditional n-doped lateral boundary.